The subject invention pertains to polyurethane foams prepared from polyol dispersions having as the dispersed phase solids derived from polyisocyanate polyaddition. More particularly, the subject invention pertains to a process for preparing such foams wherein a carboxylic acid is added to the polyol dispersion prior to reaction with isocyanate to produce polyurethane foams. The invention further pertains to a method for reducing and/or stabilizing polyisocyanate polyaddition polymer polyol dispersion viscosity.
Polyurethane foams are well established items of commerce. Such foams are generally prepared by the reaction of a polyisocyanate, i.e. an organic isocyanate having two or more isocyanate groups per molecule, with a polyol, generally a hydroxyl functional polyoxyalkylene polyether polyol. By controlling the functionality of the isocyanate and the molecular weight and functionality of the polyol, polyurethane foams ranging from exceptionally soft, flexible foams to quite rigid foams may be prepared.
In order to increase the mechanical properties of polyurethane foams, it has become commonplace to utilize polyols containing dispersed solids. Common polyol dispersions are, for example, the so-called "graft polyols" which are stable dispersions of vinyl polymers, generally homopolymers or copolymers of acrylonitrile and styrene. Such polyols can increase the load bearing capacity of polyurethane foams, for example, when used as the sole polyol component or in admixture with conventional polyether polyols. Other polyols, for example polyester polyols may be added to these mixtures as well, as can also chain extenders such as short chain diols, diamines, or alkanolamines.
Recently, polyol dispersions containing polyisocyanate polyaddition products as the dispersed phase have become commercially available. These dispersion are prepared, for example, by reacting a polyisocyanate with itself or an active hydrogen compound, generally in situ in a polyol. Thus isocyanates may be reacted with themselves (trimerized) to form polyisocyanurate (PID) dispersions; with hydrazine to form polyhydrazodicarbonamide (PHD) dispersions; with amines to form polyurea dispersions (PUD); with alkanolamines to form polyurethane urea dispersions and with primary hydroxyl polyols to form polyurethane dispersions (PURD). When reacted with di- and trialkanolamines, the dispersions are termed PIPA polyols by those skilled in the art. Such polyisocyanate addition products, used in its general sense to include all of the above dispersions (PID, PUD, PHD, PURD, PIPA) may have shorter process cycles than graft polyols and be more economical to produce. The properties of foams prepared from such dispersions also have different physical properties, in particular enhanced fire retardancy, and in general may require different formulations.
According to US-A-4,994,503, stable dispersions consisting of a continuous phase (a) such as, for instance, polyether, polyester and/or polycarbonate polyols and discrete polymer particles (b) can be produced without the use of organic polyisocyanates. To prepare polymer particles containing a plurality of aminocarbonyl or aminothiocarbonyl units, compounds containing carbonyl or thiocarbonyl groups, e.g., urea, biuret, polycarboxylic acids, and polycarboxylic acid esters, anhydrides or chlorides, can be reacted with polyamines. This reference gives no teaching as to how to incorporate a carboxylic acid into the dispersions in order to control a chemical, physical or mechanical property.
It has been discovered that many polyisocyanate polyaddition polyol dispersions exhibit changing viscosities following preparation. In particular, the viscosities may increase with respect to time. Low and constant viscosities are desirable. It has further been found that polyurethane foams prepared from such dispersions produce tight foams which may also shrink after foaming. To overcome these drawbacks, special silicone surfactants and narrow formulation ranges have been required. In some cases, in addition to water as a reactive blowing agent, air frothing of the unreacted polyol/polyisocyanate mixture is necessary. Such procedures have limited the commercialization of these polyols or increased processing and equipment costs.
It has now been surprisingly discovered that the addition of mono- and dicarboxylic acids corresponding to the formula
R-[COOH]n
where n is 1 or 2 and wherein R is a C1-C18-alkyl group when n=1 and a C1-C18-alkylene groups when n=2 to a polyisocyanate polyaddition polyol dispersion enables the preparation of polyurethane foams which do not shrink or in which shrinkage is reduced, and are more open celled in flexible foam formulations than in the absence of the carboxylic acid. When the carboxylic acid is added to the polyisocyanate polyaddition polyol dispersion shortly after manufacture, an additional benefit is a more rapid stabilization of polyol viscosity at a reduced viscosity level.
The polyisocyanate polyaddition polyol dispersions utilized in the subject process may be prepared by conventional methods. For example, polyol dispersions containing as a dispersed phase polyisocyanurate polymers having pendant urea groups may be prepared as disclosed in U.S. patent 4,386,167; polyisocyanurate dispersions may be prepared as disclosed in U.S. patents 4,359,541 and 4,359,550; and halogenated alcohol modified polyisocyanurate dispersions may be prepared as disclosed in U.S. patent 4,326,043.
Polyurea dispersions may be prepared as disclosed in U.S. patents 4,296,213; 4,518,778; and 4,093,569. Dispersions may also be prepared by reacting an alkanolamine with a polyisocyanate in the presence of a polyether polyol, as disclosed in U.S. patents 4,452,923 and 4,374,209. Dispersions formed by reaction of an aminoplast or phenoplast with a polyisocyanate are disclosed in U.S. patent 4,260,530, while polyurethane dispersions prepared by reaction of a polyisocyanate with primary hydroxyl short chain diols are disclosed in U.S. patents 4,438,252 and 4,497,913.
PHD dispersions may be prepared as taught in U.S. 4,093,569 by reacting an isocyanate with hydrazine in situ in a polyether polyol also containing more than 4 weight percent water.
The carboxylic acids utilized by the subject invention are mono - and dicarboxylic acids having the carboxylic group attached to an alkyl or alkylene group having at least one carbon atoms. Thus, preferred carboxylic acids include acetic acid, propionic acid, butyric acid, hexanoic acid, 2-ethylhexanoic acid, and the like. Dicarboxylic acids such as butanedioic acid, azelaic acid, and adipic acid are also suitable. Surprisingly, oxalic acid, having no intervening alkylene group between the carboxylic acid groups fails to provide the same results.
The amount of carboxylic acid will vary with the chemical nature of the polyisocyanate polyaddition dispersed phase, the weight percent of the dispersed phase, and the time of addition to the polyol dispersion. Amounts of from 0.01 parts by weight to 3 parts by weight of carboxylic acid may be utilized, preferably from 0.05 parts by weight to 0.5 parts by weight, all based on 100 parts by weight of polyisocyanate polyaddition polyol dispersion. The appropriate effective amount can be readily ascertained by simple hand mix foams tests routinely practiced by those skilled in the art. To perform such tests, increasing amounts of carboxylic acid are added to polyisocyanate polyaddition polyol dispersion samples and reacted with isocyanates in hand mixes. The minimum effective amount of carboxylic acid is an amount which is just in excess of that required to prevent excessive foam shrinkage. Greater amounts of carboxylic acid generally cause greater openness of the foam structure, in some cases leading to foam collapse. However, this increased amount may be desirable nevertheless, as the polyurethane catalyst level may be increased or a more active catalyst utilized to cause more rapid gelation, thus providing a non-shrinking, open celled, high quality product.
It has been found that the amount of carboxylic acids required when the carboxylic acid is added to the polyisocyanate polyaddition polyol dispersion just prior to reaction with isocyanate or in the mix head of commercial polyurethane equipment is different than the amount required when added previously to the polyisocyanate polyaddition polyol dispersion. Thus, addition to the polyisocyanate polyaddition polyol dispersion 10 to 24 hours before use is preferred. Most preferably, the carboxylic acids are added following preparation of the polyisocyanate polyaddition polyol dispersion itself, as this time of addition generally results in the most rapid stabilization of the dispersion, generally at a lower viscosity than when addition is delayed.
The invention may now be illustrated by reference to the following examples.
A polyisocyanate polyaddition polyol dispersion was prepared by the method disclosed in U.S. patent 4,374,209 utilizing as reactants 22.5 parts diethanolamine, 18 parts triethanolamine, 1.62 parts dibutyltindilaurate (dissolved in dioctylphthalate 1:5) and 63 parts of toluenediisocyanate. The initial mix time was 10 seconds, following which an exotherm was observed which elevated the temperature from room temperature to a maximum of 50°C (122°F) after 10 minutes. The reaction was allowed to continue for 30 minutes after which the temperature had fallen to 47°C (116°F). The base polyol was a glycerine and propylene glycol initiated polyol having a functionality of 2.6, a hydroxyl number of 56, and containing 88 weight percent oxypropylene and 9.1 weight percent oxyethylene residues.
To a sample of polyisocyanate polyaddition polyol dispersion as prepared in Example 1 was added 2-ethylhexanoic acid in an amount of 0.593 mg/g (Example 2). A sample was also left untreated (Example 2A) . A commercial polyisocyanate polyaddition polyol dispersion similar to that prepared in Example 1 was obtained and similarly treated (Example 3). A control was left untreated (Example 3A). Viscosity in all samples was measured at various time intervals at 25°C utilizing a Brookfield viscometer. The results are presented in Table I below.
As can be seen from the table, addition of the carboxylic acid results in both a lower viscosity product as well as more rapid viscosity stabilization. The effect is greatest when the carboxylic acid is added of the polyisocyanate polyaddition polyol dispersion immediately following preparation, however is still effective even with previsously prepared polyisocyanate polyaddition polyol dispersions.
In the foam examples which follow, the following raw ingredients are utilized.
- DC-5043
- a silicone surfactant available from Dow Corning.
- B-4113
- a silicone surfactant available from Goldschmidt, A.G.
- Dabco 33-LV
- an amine catalyst available from Air Products and Chemicals Inc.
- Niax A-1
- an amine catalyst available from Union Carbide Chemical Co.
- T-12
- dibutylindilaurate
- 2-EHA
- 2-ethylhexanoic acid
- DEOALF
- diethanolamine 85 wt.%, water 15 wt.%
- FR
- tris[1,3-dichloropropyl]phosphate; flame retardant
- Antiblaze 100
- bis[chloroalkyl]phosphate ester; flame retardant supplied by Albright & Wilson Americas, Inc.
Flexible foam formulations were prepared using as the polyol component the polyisocyanate polyaddition polyol dispersion of Example 1. Each formulation contained, in parts by weight, 300 parts polyisocyanate polyaddition polyol dispersion, 7.5 parts Antiblaze 100, and TDI (toluene diisocyanate) at 100 index. The remaining ingredients, physical properties, and comments are as follows:
A foam was prepared utilizing as the polyol component a hydrolyzed polyisocyanurate dispersion (PID) polyol in the mount of 120 parts, and 180 parts of the same polyether polyol used to prepare the polyisocyanate polyaddition polyol dispersion of Example 1. The formulation was otherwise as in Examples 11-16. Example 17 contained non 2-ethylhexanoic acid (2-EHA) while Example 18 contained 0.54 parts acid. The foam without 2-EHA shrunk severely while that containing 2-EHA exhibited much less shrinkage, showing that a larger processing window is available with this PID polyol when the carboxylic acids of the invention are added. The foams prepared with the without 2-EHA were clearly different. while not wishing to be bound by theory, this may be due to complete reaction of the isocyanate in the PID polyol dispersion which occurred during its preparation and isolation.
Formulations as in Examples 17-18 with and without 2-EHA were prepared but utilizing Multranol® polyol 9151 instead of the hydrolyzed PID polyol. Example 17 produced an acceptable but tight foam while Example 18 with 2-EHA added showed total collapse, again illustrating greater processing latitude.
Machine runs were made with formulations similar to the preceding examples containing various levels of diethanolamine, and 2-ethylhexanoic acid blended with the silicone stream, blended with the flame retardant stream, and blended with the polyisocyanate polyaddition polyol dispersion 12 hours before running. Foams were also prepared without addition of acid. Diethanolamine is a desired additive in high resilience foams as it tends to decrease foam hardness while increasing the sag factor. The results of these tests, employing 0.18 parts 2-ethylhexanoic acid per 100 parts polyisocyanate polyaddition polyol dispersion in a 28.8 g/l (1.8 pound/ft3) foam at 100 index, indicate the following:
- a) Foams prepared without 2-ethylhexanoic acid have poor processability at 28.8 g/1 (1.8 pcf) density;
- b) Addition of 2-ethylhexanoic acid at the mix head, whether blended with silicone or flame retardant, produced unstable foam (collapse) which may be overcome through change in catalyst; and,
- c) Addition of 2-ethylhexanoic acid to the polyisocyanate polyaddition polyol dispersion 12 hours before use produced good foam with a processing latitude with respect to addition of diethanolamine.